This invention relates to a method and apparatus for determination of settlement in terrestrial environments such as the foundations of buildings or other structures by a system in which the elevation, referenced to a datum, of any point along the length of a small bore tube and incorporated into a foundation structure is determined. The tube is typically several thousands of feet in length and of nylon and incorporated during construction of a building, structure or embankment. The purpose being principally to evaluate the nature and degree of progressive settlement due to natural consolidation or externally influenced consolidation due to loads such as in dams, or foundation undermining. In such a system an interface between two immiscible liquids of considerably different densities (mercury and water) is advanced along the tube and from that it is possible to determine, by suitable measurement, the elevation of the interface. The background in the art of the invention is further explained in conjunction with FIG. 1 of the accompanying drawings wherein the one end of tube T has a reservoir R for mercury maintained at a constant elevation A and the other end of the tube has a pressure measuring gauge G. The tube has water W towards the other end and mercury M towards the one end with an interface I. The two liquids give considerable different hydraulic pressures per unit column height (5.91 p.s.i./foot for mercury and 0.43 p.s.i./foot for water and the pressure at the interface I is due to the mercury column is +5.91 p.s.i./foot and that due to water+ 0.45 p.s.i./foot, if the height of the head is h then the pressure shown by gauge G will be 5.91 h-0.43 h=5.84 h p.s.i. If the interface level is changed with respect to elevation A, gauge pressure will change by 5.48 p.s.i./foot of interface elevation change, increasing as h increases.
An object of this invention is to provide an improved method and means to give more accurate results.
Another object is to provide a novel construction of back pressure unit.